Method of preventing wax deposits in tubing



Patented Dec. 1, 1942 METHOD OF PREVENTING WAX DEPOSITS IN TUBING Clarence J. Coberly, Los Angeles, Calif., assignor to Kobe, Inc., Huntington Park, Calih, a corporation of California No Drawing. Application August 1, 1940, Serial No. 349,226

1 Claim.

Myinvention relates to the transmission of petroleum oils through pipes or other conduits, and more particularly to the transmission of petroleum oils containing waxes. Petroleum oil as used herein denotes crude oil as produced from the ground or any fluid derived from such crude oil. Wax as used herein denotes any substance, for example, parafiine, which crystallizes or solidifies at a critical temperature, hereinafter called the crystallization point. Many petroleum oils contain paraffines, asphaltenes, and the like, which have a relatively low temperature of crystallization or crystallization point.

When a petroleum oil containing wax is passed through a pipe or conduit the inner wall of which is at a temperature below the crystallization point of the wax, wax tends to deposit on such walls in sufi'icient amounts to materially reduce the free area inside the conduit through which the oil must pass, thus retarding the flow of the oil.

It is an object of my invention to prevent such deposition from petroleum oils which have a considerable wax content.

The waxes found inmost petroleum oils crystallize or solidify at a temperature of from 95 F. to 130 F., although certain petroleum oils contain waxes whose crystallization point is outside this range, which is merely given as that including many petroleum oils from which wax deposition may be expected. The crystallization point of the wax contained in any such oil can be read ily determined by one skilled in the art by cooling a film of oil and watching for wax crystals with a microscope, or by centrifuging a cooling oil and noting the temperature at which wax crystals are thrown out of the oil.

The usual method of preventing wax deposition is to maintain the oil at a temperature above the crystallization point, so that the wax will remain in solution in the oil. This method results in a heavy deposition of wax on any surfaces having a temperature below the crystallization point of the wax.

I have discovered that this deposition can be retarded or prevented by using other methods. Even if an oil carries a comparatively large wax content, wax deposition will be retarded on the walls of any conduit through which it flows if the oil is at a lower temperature than said walls even though the walls are at a temperature below the crystallization temperature of the wax if the wax is carried in the oil in the form of small solid particles in suspension. For example, an oil containing wax having a crystallization temperature of 130 F., if initially cooled substantially below that temperature, can be carried through a pipe having an even lower temperature with little or no deposition of wax.

Many oils contain difierent waxes or a series 7 of waxes each of which has adifferentcrystallization point. For example, some of the wax in an oil may crystallize at 130 F. but all of the wax will not crystallize until the oil has been held at a temperature of F. I have found that if such oils are cooled to a temperature slightly below F., some crystals are formed and that as the oil is further cooled, very little deposition on the walls of any conduit occurs, even though the oil is still further cooled during its passage through the conduit. I believe this is due to the presence of preformed crystals in the oil, each of these crystals forming an active nucleus about which all further crystals form in preference to forming on the inert walls of the conduit. I have found further that by introducing into the oil small particles of resin or other foreign matter these particles form nuclei around which the wax crystallizes in preference to crystallizing on the wall of the conduit or container.

The method of using my invention to prevent deposition on the wall of a conduit or container of wax crystals from an oil is to first determine roughly the crystallization point of any wax carried in the oil. The oil is then cooled to a temperature somewhat below this point preferably by blowing cold gas through it. As the temperature of the oil falls, wax crystals are formed and the oil containing such crystals can be circulated through conduits having an even lower temperature with little or no wax deposition on the walls of the conduits.

A better method in some cases is to introduce fine particles of resin, having a melting point above the crystallization point of the wax, into the oil, each particle of resin acting as a nucleus about which crystallization can occur, the nucleus with its load of wax crystals being carried in suspension in the oil with little or no deposition on the walls of the conduit.

I claim as my invention:

The method of retarding wax deposition, from an oil containing wax, on the walls of a conduit through which the oil is carried, the wax being of such a nature that it forms small crystals when cooled below the crystallization temperature of the wax, which comprises: providing said oil with small particles of a substance not normally present in such an oil, carried in suspension in the oil, said particles being of a nature to promote crystallization of said wax about said particles; cooling said oil during its passage through the conduit to a sufiicient degree to cause deposition of wax crystals on said particles; and withdrawing the oil from the conduit with the greater portion of said particles still in suspension therein.

CLARENCE J. COBERLY. 

